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Why post this? Because it's good to expand your mind. I've noticed that many posters are either unfamiliar with common logical fallacies, or are unsure of the details, and are thus unsure of how to respond or refute such arguments when they are presented, or are unable to recognize such fallacies in their own posts. And spotting such things is a useful skill, above and beyond simply arguing with other freepers - one who becomes familiar with informal fallacies will often be surprised and dismayed to learn just how often logical fallacies are employed by politicians. Spotting when someone is handing you a "bill of goods" is more than simply an academic skill - it's a virtual necessity in this day and age.

And so I thought it might be useful to present an authoritative collection of common logical fallacies, of the type often encountered on the web and elsewhere. These are derived from Chapter 6 of Copi and Cohen's excellent text, Introduction to Logic, 10'th edition - it is a preferred text for many introductory college logic courses, due to its relatively clear and accessible style. I plan for this to be an ongoing series, covering the fallacies that are exposed therein - although they list seventeen fallacies, and I intend to cover all seventeen, some sections are somewhat shorter than others, so I may decide to combine them into a single posting. Finally, I have, for the most part, eliminated footnotes from the sections, except where I deem them to be particularly useful.

As I said, I intend to post all the parts over the coming days, whether there's any expressed interest or not. I hope that freepers will find it worthy of discussion - feel free to post examples of fallacies spotted "in the wild", or ask questions of others, and so forth - but even if not, I think it will be useful as a reference for the future. If there does prove to be sufficient interest, let me know, and I will put together a ping list for future installments in this series.

I maybe had too much eggnog at the office Christmas party (hic!) but I don't think that the "reasonable doubt" standard is an argument from ignorance.

Putting it into a nutshell, depending on the type of case, there are different ways that the burden of proof is allocated. In a civil case, the plaintiff has the burden of proof, and for most civil cases, the standard is "preponderance of the evidence." If the plaintiff proves that his version of the facts is more likely than the defendant's version, he prevails.

When you think of it, think of Justice holding her scales. They don't have to tip very much for the plaintiff to win, but if they are in equipoise, the plaintiff hasn't met the burden of proof and doesn't win.

In fact, the judge may not even force the defendant to put on evidence if the plaintiff's evidence isn't sufficient, but may dismiss the case on a motion to strike the evidence as being insufficient to make the case as a matter of law.

But if the plaintiff gets past the motion to strike, then the burden shifts to the defendant to prove his or her case.

In a criminal case, it works the same way, but the amount of weight that needs to be placed on the scales is far heavier. The plaintiff in a criminal case is the government, because a crime is an offense against the government. And the amount of weight that needs to be placed on the scales of justice in order to get past a motion to strike is far, far heavier than the 1% that is needed in a civil case. How much? There is not a percentage, but the evidence needs to be really, really strong. Strong enough that all by itself, without more, it's enough to meet the "reasonable doubt" standard in the mind of the judge.

It's called "reasonable doubt" because the standard doesn't require you to consider anything that's outside the scope of reason, such as aliens coming down and committing the crime.
Otherwise, the case doesn't go forward, but goes out on a motion to strike.

But if the case gets past the motion to strike, then defendant doesn't have to put on any evidence, but can let the jury decide based on the same evidence that the trial judge ruled was sufficient to get past the motion to strike.

This doesn't require the jury to be ignorant, but to have higher standards in a criminal case. If there are equally plausible explanations which are consistent with the facts and the evidence that mean that the defendant's innocence is a real possibility, then that should be sufficient to create reasonable doubt.

But a defendant in a criminal trial isn't found "innocent," he's found "not guilty." If it really were the same as "argument from ignorance," the failure to prove guilt would mean a finding of innocence. I think maybe in Scotland there is a finding of innocence but not in the USA or England.

I think fallacies are overrated. I've been thinking of writing a book called "In Praise of Fallacies", or "My Favorite Fallacies", or "Fallacies We Can't Live Without" or somesuch. It would explain why some of the standard logical fallacies are actually indispensable in the real world.

I thought of this when I discovered to my horror that "the slippery slope" is considered a fallacy! This may be true in a strict deductive sense, but in order to make sense of the real world, you have to use a combination of deduction & induction, and place your bets accordingly. Things like the slippery slope (basically making a small concession to the opposition's argument, when the point being conceded turns out to imply a fundamental opposition point after all), or appeal to authority, or its flip side: ad hominem, can all be good tools to use in the face of real-world uncertainty.

The textbook article seems to recognize this somewhat, at least implicitly. I wonder how many formal fallacies are actually quite useful in this way?

(p.s. I'm sure I'll never get around to writing "In Praise of Fallacies", so anyone who wants to run with the idea, go for it. Mention me in the Acknowledgements. :-)

Similarly, when a security investigation yields no evidence of improper conduct by the persons investigated, it would be wrong to conclude that the investigation has left us ignorant. A thorough investigation will properly result in their being "cleared." Not to draw a conclusion, in some cases, is as much a breach of correct reasoning as it would be to draw a mistaken conclusion.

This is a liberal favorite; no amount of proof will suffice to win an argument with them. There will always be some "third way" pie-in-the-sky that will in future rescue their argument.

I use the example of the time I demonstrated a trick to my dad, and he snorted, "Once in a million!" I repeated the trick and he retorted, "Twice in two million!"

On any given issue any given person controls his own individual burden of proof; if you have faith that the earth is flat, then flat it will--at least in your own mind--remain. If on the other hand you have faith that the other person is illogical, then illogical they will--at least in your own mind--remain, mountains of evidence to the contrary notwithstanding. I would in fact suggest that our individual character is largely defined by what burden of proof we establish for propositions of various sorts.

PHILOSOPHY PING

(If you want on or off this list please freepmail me.)

Ad ignorantiam fallacy - (argument from ignorance). Asserting the truth of any proposition on the basis that what is asserted has never disproved or what is denied has never been proved; or that there is no evidence for the thing denied, or, against what is asserted.

Debate about the mystic, paranormal, or occult proceed largely by arguing ad ignorantiam. The fallacy also forms the basis for most medical quackery tricked up with a lot of medical jargon.

Examples:

"It has never been proved, nor can it be, that clairvoyance does not exist, therefore, it must exist." "It has never been proved, nor can it be, that clairvoyance exists, therefore, it cannot exist."

"Studies show that many people using fibrilopymesium hypochloride recover completely from their diseases. No study has ever failed to show this." There is no proof it doesn't work, therefore it must work. "Studies show that some people using fibrilopymesium hypochloride never recover from their diseases. Every study shows this." There is no proof it does work, therefore, it must not work.

Argument from ignorance is obviously very useful.

Hank